\U`ro*pyg"i*al\, a. [See {Uropygium}.] (Anat.)
Of or pertaining to the uropygium, or prominence at the base
of the tail feathers, in birds.
{Uropygial gland}, a peculiar sebaceous gland at the base of
   the tail feathers in most birds. It secretes an oily fluid
   which is spread over the feathers by preening.